Method for desizing artificial silk



Fresco; m

Buffalo Bufialo, N. Y.

Electro Chemical ,"Qompany, Inc.,

No Drawing. Application June 8, 1939, Serial No.

278,167. In Germany March 31, 1937 3 Claims.

It is known that the sizing of artificial silk, cellulose wool, and mixed spun yarn, particularly of acetate silk, is effected mainly with linseed oil or products containing linseed oil. .However, since linseed oil size possesses a tendency to resinify and harden, desizing presents great difficulties, particularly when the fibers have been stored for some time or have been exposed to the action of light and heat.

Desizing of fibers sized with linseed oil is generally efiected by means of alkali, particularly sodium carbonate. But this method has the disadvantage that on the one hand one is forced to use rather high concentrations of alkali, particularly when the size has aged; on the other hand one has to keep the concentration of alkali as low as possible to prevent the alkali from attacking the acetate or viscose fibers, respectively, by a process of saponification or dissolution, respectively.

It is thus necessary to carry through the desizing process within a definite range of alkali concentration. Any excess of alkali above or below specified limits set results either in destruction of the fiber or in insufiicient desizing thereof.

It has been proposed heretofore to add peroxides to the desizing washing liquor, as, for instance, hydrogen peroxide, sodium perborate, as well as borax, soap, certain oils, and others. But none of these agents have made it possible to carry through complete and rapid desizing without risk of damage to the fiber.

Experiments of the applicant have shown the possibility of carrying through desizing with a higher content of alkali than usual heretofore without fear of damage to the fiber.

While prior to the present invention the desizing Washing liquors for acetate fibers were not allowed to contain more than 0.25 gram per liter of soda and for viscose fibers no more than 2 grams per liter, it is now possible to use up to 10 grams per liter of soda subject to provision being made that the desizing liquor be given at the same time additions of hydrogen peroxide and bicarbonate, e. g., sodium bicarbonate. Instead of soda caustic alkali, e. g., caustic soda, or a mixture of alkaline carbonate and caustic alkali may be used. The content of bicarbonate may be increased to about 10 grams per liter, the content of hydrogen peroxide to about 2 grams per liter (40%) But normally one will find 1-5 grams of soda, 1-5 grams of bicarbonate, and 0.5-1 gram of hydrogen peroxide per liter satisfactory. Instead of soda, also up to 2 grams per per liter of soda and 0.2-1 gram per liter of caustic soda may be used, it being a rule that the content of alkali may be chosen the higher, the greater the content of bicarbonate.

The temperature of the washing liquor may be increased up to 80 C.; but generally it is sufficient to Work at C. With acetate silk the temperature must not be more than C.

The time of processing or treatment varies according to the kind and amount of size. Normally it is about one hour. But after at least two hours, even badly hardened size should be removed without leaving any residue.

The fact that no saponification or dissolution of the fiber, respectively, takes place, in spite of the high content of alkali, is due to the fact that the pH value of the liquor is reduced by the presence of bicarbonate. On the other hand, however, the amount of alkali present is so great that the desizing proceeds easily and completely.

Furthermore, it appears that the content of bicarbonate of the liquor involves an extremely good bufiering of the solution. This means that during the desizing process the pH value of the solution remains practically constant. Therefore not too strong an alkalinity can be present causing the fiber to be damaged. On the other hand, the alkalinity cannot drop to such a degree as to render the desizing insufficient.

Contrary to the above, the desizing liquors known heretofore show very bad buffering. Thus there is always the risk with these washing liquors that the alkalinity might change above or below the admissible limits.

A further advantage of the new method consists in brightening up of the artificial fibers apart from desizing. Consequently with subsequent dyeing of the fibers, particularly with delicate shades, an excellently clear tone of coloration is obtained.

Naturally the application of the new method is not limited to the pure viscose or acetate fibers and their mixtures, but equally to mixtures of artificial fibers with fibers of vegetable or animal origin.

What I claim is:

1. The method of desizing goods containing artificial silk sized with linseed oil which comprises treating the goods in an aqueous desizing bath comprising 1-5 grams sodium bicarbonate per liter, an amount of sodium carbonate per liter between 1-5 grams sufficient if alone to damage the artificial silk and 0.5 to 1 gram of hydrogen peroxide per liter, the carbonate and biliter of caustic soda or a mixture of 2-5 grams 55 carbonate being present in sufficient quantities QLAHL'H HOOM that the pH of the solution is less than that due to carbonate alone, and to bufier the solution, the temperature of treatment being below about 80 C.

2. The method of desizing goods containing artificial silk sized with linseed oil which comprises treating the goods in an aqueous desizing bath at a temperature of below about 80 C., the bath containing up to 2 grams per liter of peroxide, sodium bicarbonate and a strong alkali suflicient in concentration if alone to damage the artificial silk selected from the group consisting of caustic soda and soda ash, the amount of bicarbonate being sufiicient to lower the pH due to the strong alkali alone and to buffer the solution so that substantially no change in pH is produced during the desizing operation.

3. The method of desizing goods containing artificial silk sized with linseed oil which comprises heating the goods in an aqueous desizing bath at a temperature of below about 80 C., the bath containing up to'2 grams per liter of hydrogen peroxide, sodium bicarbonate and a strong alkali sufiicient in concentration if alone to damage the artificial silk selected from the group consisting of caustic soda and soda ash, the amount of sodium bicarbonate being sufiicient to lower the pH due to the strong alkali alone and to buffer the solution so that substantially no change in pH is produced during the desizing operation.

, ANNA NODER. 

